1. Field of the Invention
The present invention relates to an optical recording medium such as an optical disc, and more particularly, to a method for evaluating anti-contamination level on a surface of the optical disc. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for quantizing the characteristic of a protective coating film being formed on the surface of an optical disc, so as to enhance the stability thereof.
2. Discussion of the Related Art
Generally, an optical disc is used for recording information on the surface of the optical disc by using laser beam. More specifically, the optical disc is a high-capacity data storage means having audio, video, and text information converted to digital signals, then, a low intensity laser beam is projected thereto so as to carry out a reading of the optical disc by acknowledging the different intensities of the reflected light. Optical disc media include compact discs (CDs), digital video discs (DVDs), laser discs (LDs), and so on. And, recently, blu-ray discs (BDs) and advanced optical discs (AODs) have been in active and competitive development as a standard for the next generation storage means.
The blue-ray disc has been under development to target the high definition video disc recorder (HDVDR). The blu-ray disc is considered to be the next generation optical disc storage means using a bluish-purple semiconductor laser (BPSL). Accordingly, the blu-ray disc has a storage capacity of 27 gigabytes (GB), which corresponds to a 13-hour running time of regular film and a two-hour running time of visual material having high definition television (HDTV) picture quality. As described above, interest and focus on the blu-ray disc as the next generation storage means that can compensate the shortcomings of the conventional DVDs are elevating. However, due to the fine signal characteristics of the blu-ray disc, quality deficiency resulting from scratches, deformities or formation deficiencies, fingerprints, adhesion of impurities during fabrication process, and so on may occur. Therefore, after the fabrication of the blu-ray disc is completed, a quality inspection process is performed, and the inspected product is then shipped to the market.
Generally, the related art optical disc quality inspection process is performed by four (4) measuring drives. Provided that a plurality of optical discs fabricated from the same fabrication device all have the same characteristics, the manufacturer randomly selects an optical disc and mounts the selected optical disc on the measuring system. The first measuring drive measures high frequency signals and jitter from the optical disc. The second measuring drive measures servo signals (i.e., focusing error signals and tracking error signals) based on signals reproduced from the optical disc. The third measuring drive detects the mechanical characteristics of the optical disc presently being under quality inspection. Finally, the last (or fourth) measuring drive detects the optical characteristics of the optical disc.
As described above, the related art optical disc quality inspection process consists of inspecting the accuracy in information recording, the mechanical and optical characteristics of the optical disc, and so on. Chemical and physical contamination, such as fingerprints, that may occur on an incident surface of a laser beam for recording/reproducing information, during the usage of the high density optical disc, may result in a deterioration of optical disc signals, damage in data, as well as incapacity of recording and/or reproducing information on the disc. Therefore, in order to prevent such problems from occurring, a protective coating film is formed on the surface of the disc, so as to enhance the level of anti-contamination or surface stability, and the optical disc is inserted in a cartridge so as to protect the disc from contamination. Recently, however, discs having only the protective coating film formed thereon and no cartridges, in order to minimize the volume of the disc, have been introduced to the market. Therefore, the quantization of anti-contamination of the protective coating film formed on the surface of the disc has become an important factor for effective fabrication and usage of a disc.
Nevertheless, a quantized method for evaluating anti-contamination occurring on the surface of a high density optical disc has not been developed in the related art. In the related art, the level of anti-contamination is evaluated solely by the personal judgment of an extensively experienced manufacturer, whose judgment is based on observing the amount or level of an actual fingerprint or a contaminant being adhered or smeared to the surface of the disc. Therefore, when inspected through the above-described related art anti-contamination level evaluation method, some misjudgment may occur and deficient discs that were subject to such misjudgment may be shipped to the consumer market.